Nigerian oil officials have called for talks with striking workers, in a bid to end the threat of mounting industrial action.

Nigeria's Department of Petroleum Resources has invited workers of the senior staff union, Pengassan, for a meeting over complaints of pay and conditions.

Pengassan staff began a strike on Monday in support of demands including greater autonomy, higher pay, and payment of allowances arrears, some dating back to 2000.

Blue-collar staff at the DPR on Tuesday joined the strike, which has threatened Nigeria's oil output of more than 2 million barrels a day.

Fresh mandate?

Bayo Olowoshile, Pengassan's deputy national secretary-general, said the outcome of the meeting with DPR heads would determine the union's "next line of action".

"If it is the usual rhetoric that they are making efforts to solve the problem, it won't help matters.

"But if the DPR has been given a fresh mandate, then fine because we want results."

Earlier attempts by the Nigerian government to halt the strike have failed.

An energy adviser of Nigeria's president. Olusegun Obasanjo, offered to meet protested on 25 February.

But the strikers declined, saying the date did not reflect the urgency of their demands.

Panic buying

Pengassan members monitor the quantity and quality of crude leaving Nigerian terminals, and some observers have said the strike threatens to cripple the country's export capability.

"The operation of the DPR is grounded," said Joseph Akinlaja, secretary general of the Nupeng union.

"Nothing is happening at the terminals and offices.

"The strike is proving its point. It's been very effective."

There were reports of long queues of cars at petrol stations in Lagos, the country's commercial capital, and the capital Abuja, as panic buying of petrol began.

But oil giant Shell, which accounts for about half of Nigerian oil production, said shipments were continuing "undisrupted", as senior managers took over posts from striking workers.

And a spokesman for ChevronTexaco said: "We have not received any complaints that ships due for loading have failed to load, so I can say there have been no disruptions at the terminal."

A long-running strike could have severe repercussions for the Nigerian economy, as oil exports account for more than 80% of government revenue and more than 90% of foreign exchange earnings.